What lithium-ion batteries do in electric cars

A lithium-ion battery is a rechargeable pack that stores electrical energy and releases it to power an electric motor. Unlike the small battery in a gas car that only starts the engine, the battery in an electric car is the entire fuel system — it holds enough energy to move the vehicle 200 to 400 miles on a single charge, depending on the car's size and efficiency.

The battery sits underneath the car's floor, usually running the full length of the wheelbase. When you plug in to charge, electricity flows into the battery and is stored as chemical energy. When you drive, that chemical energy converts back to electrical energy, which the motor uses to turn the wheels. The battery also captures energy when you brake — a process called regenerative braking — and stores some of that energy back into the pack.

Lithium-ion technology became the standard for electric cars because it holds more energy per pound than older battery types, charges faster, and lasts longer before needing replacement. A typical car battery today will retain 80 to 90 percent of its capacity after eight to ten years of normal use.

Key Takeaways

  • Lithium-ion batteries store chemical energy that converts to electrical power for the motor, and they sit underneath the car rather than under the hood.
  • Battery capacity is measured in kilowatt-hours (kWh), and a larger capacity means longer driving range before you need to recharge.
  • Charging speed depends on the charger type — Level 1 (household outlet) takes 24 hours or more, Level 2 (240-volt) takes 4 to 10 hours, and DC fast chargers add 200 miles in 20 to 30 minutes.
  • Batteries degrade slowly over time but typically retain most of their capacity for eight to ten years, and replacement costs range from $5,000 to $15,000 depending on the car model.
  • Cold weather reduces range temporarily because the battery chemistry slows down, but the battery itself is not damaged.

How battery capacity and range connect

Battery size is measured in kilowatt-hours (kWh), which describes how much electrical energy the pack can hold. A small electric car might have a 40 kWh battery, while a larger SUV could have 100 kWh or more. The bigger the battery, the farther the car can travel on one charge.

However, the relationship between battery size and real-world range is not one-to-one. A car's efficiency — how much energy it uses per mile — depends on the motor design, weight, aerodynamics, and driving conditions. A lightweight sedan with a 60 kWh battery might go 250 miles, while a heavier SUV with the same battery might go 200 miles. Manufacturers publish an EPA-estimated range for each model, which is based on standardized testing and is usually close to what you will see in normal driving.

Range also changes with weather, driving style, and road conditions. Cold temperatures reduce range by 20 to 40 percent because the battery chemistry slows down and the car uses extra energy to heat the cabin. Highway driving at high speeds uses more energy than city driving. Hilly terrain uses more energy than flat roads. These are temporary effects — the battery is not damaged, and range returns to normal when conditions change.

The three types of chargers and how long charging takes

Level 1 chargers plug into a standard 120-volt household outlet, the same outlet you use for a lamp. They add about 2 to 5 miles of range per hour of charging. A completely empty battery might take 24 to 48 hours to fully charge on Level 1. Most owners use Level 1 only as a backup or for topping up overnight if they have a short commute.

Level 2 chargers require a 240-volt circuit, the same voltage as an electric dryer or oven. They add 10 to 30 miles of range per hour, depending on the charger's power output and the car's onboard charging equipment. A typical Level 2 charger fully charges a 60 kWh battery in 4 to 10 hours. Most home installations and public charging networks use Level 2. If you charge overnight at home, Level 2 is usually sufficient for daily driving.

DC fast chargers bypass the car's onboard charger and deliver power directly to the battery at much higher voltage. They add 150 to 200 miles of range in 20 to 30 minutes, though charging speed slows as the battery approaches full capacity. DC fast chargers are found at highway rest stops and commercial charging networks. They are useful for long trips but are not practical for daily home charging because the infrastructure is expensive and the high power output generates heat that can stress the battery if used constantly.

How battery degradation works and what replacement costs

All lithium-ion batteries lose capacity over time. After one year of normal use, a new battery might retain 95 to 98 percent of its original capacity. After five years, it typically retains 90 to 95 percent. After eight to ten years, most batteries are at 80 to 90 percent of original capacity. This gradual loss is normal and does not mean the battery is failing — the car straightforward has a slightly shorter range than it did when new.

Degradation happens because the chemical reactions inside the battery are not perfectly efficient. Each charge cycle causes microscopic damage to the battery's internal structure. Heat accelerates this damage, which is why batteries in hot climates degrade faster than those in cool climates. Charging to 100 percent frequently also speeds degradation compared to charging to 80 percent most of the time.

Battery replacement is expensive. Costs range from $5,000 to $15,000 depending on the car model and battery size. However, most manufacturers cover the battery under warranty for eight years or 100,000 miles, whichever comes first. Some cover it for ten years or 120,000 miles. If the battery fails within the warranty period, the manufacturer replaces it at no cost to you. After the warranty expires, replacement is your responsibility, though many owners keep their cars long enough that the battery never needs replacement during their ownership.

What happens inside a lithium-ion cell

A lithium-ion battery is made of thousands of small cylindrical or pouch-shaped cells, all connected together. Each cell contains two terminals called the anode and cathode, separated by a chemical substance called an electrolyte. Lithium ions move back and forth between the anode and cathode through the electrolyte, and this movement of ions is what creates electrical current.

When you charge the battery, electrical current pushes lithium ions from the cathode to the anode, storing energy as chemical potential. When you drive, the ions flow back from the anode to the cathode, releasing that energy as electrical current that powers the motor. The electrolyte allows ions to move but prevents electrons from crossing directly, which forces the electrons to flow through the external circuit — the motor, wiring, and other car systems — where they do useful work.

Different battery chemistries use different materials for the cathode. Lithium iron phosphate (LFP) is durable and safe but stores less energy per pound. Nickel-based chemistries store more energy per pound but are more sensitive to heat and overcharging. Manufacturers choose the chemistry based on the car's intended use — a long-range sedan might use nickel-based chemistry, while a commercial delivery vehicle might use LFP for durability and safety.

Cold weather, heat, and battery performance

Cold temperatures slow the chemical reactions inside the battery, which temporarily reduces the power the battery can deliver and the energy it can store. In freezing weather, you might see a 20 to 40 percent reduction in range. The battery also charges more slowly in cold weather because the internal resistance increases. However, this is temporary — once the battery warms up, performance returns to normal. Cold does not permanently damage a lithium-ion battery.

Heat is more damaging than cold. Sustained high temperatures accelerate the chemical degradation that causes capacity loss. A battery that spends years in a hot climate will degrade faster than an identical battery in a cool climate. This is why some cars with large batteries include active cooling systems that circulate coolant through the battery pack to keep it at an optimal temperature, especially during fast charging or in hot weather.

Most electric cars have thermal management systems that protect the battery in extreme conditions. In very cold weather, the car may preheat the battery before you drive, using some stored energy to warm it up. In very hot weather, the cooling system works harder to keep the battery from overheating. These systems use a small amount of energy but extend battery life significantly.

Recycling and second-life uses for old batteries

When an electric car battery reaches the end of its useful life in a vehicle — typically when capacity drops below 70 to 80 percent — it still holds substantial energy and can be repurposed. Many recycling programs remove the battery from the car and test it to see if it can be used in a stationary energy storage system, such as a backup power supply for a building or a grid storage facility. These second-life batteries can operate for another five to ten years in applications that do not require the full performance of a new battery.

When a battery can no longer be used for any purpose, it goes to a recycling facility where the cells are disassembled and the materials — lithium, cobalt, nickel, and others — are extracted and refined. These recovered materials are then used to manufacture new batteries, reducing the need to mine virgin materials. Recycling recovers 90 to 95 percent of the battery's material value.

Battery recycling is still developing as an industry because most electric cars sold in the last ten years are still in use. As more cars reach end-of-life over the next decade, recycling capacity will expand. Currently, recycling is not yet economically competitive with mining new materials in all cases, but as battery volumes increase and recycling technology improves, this is expected to change.

Frequently Asked Questions

Can you replace just part of a battery, or do you have to replace the whole pack?

In most cases, you replace the entire pack because the cells are integrated into a single unit and the management system is designed around the full pack. Some manufacturers offer module replacement for specific sections, but this is rare and usually only available through the manufacturer's service network. For most owners, replacement means a new complete battery.

What is the difference between kWh and kW?

kWh (kilowatt-hour) measures energy storage — how much total energy the battery holds. kW (kilowatt) measures power — how fast energy is being delivered. A 60 kWh battery holds 60 kilowatt-hours of energy. A 10 kW charger delivers 10 kilowatts of power. Think of it like a water tank: kWh is the tank's size, and kW is how fast water flows out of the tap.

Is it bad to charge your electric car every day?

No. Daily charging is normal and expected. Lithium-ion batteries are designed to be charged and discharged regularly. What does accelerate degradation is consistently charging to 100 percent and then when ready driving, or leaving the battery at 100 percent for extended periods. Many owners extend battery life by charging to 80 percent for daily use and only charging to 100 percent before long trips.

Do electric car batteries lose charge when the car is parked?

Yes, but very slowly. A parked electric car loses about 2 to 3 percent of its charge per month when not in use, depending on the model and temperature. This is because the battery management system, onboard computers, and other systems draw a small amount of power continuously. If you park for several months, the battery will be noticeably lower when you return, but it will not be completely empty.

Can you use a regular extension cord with a Level 1 charger?

You can, but it is not recommended for regular charging. Extension cords add electrical resistance, which generates heat and slows charging. For occasional use, a heavy-gauge extension cord is acceptable, but for daily charging, plug the charger directly into the outlet. If you need to charge far from an outlet, have an electrician install a dedicated circuit closer to where you park.